Dimensions of hex nuts, hex jam nuts, heavy hex nuts and heavy hex jam nuts are shown in the following charts according to ASME B18.2.2-1987 standard.
Hex nut is a hexagonal shape fastener which is used with a bolt to fix parts
together. Hex jam nut is a type of nut with a thinner thickness with respect to
a hex nut. Jam nut is generally used to lock a standard nut to prevent
loosening and secure it in place.
Heavy hex nuts and heavy hex jam nuts are slightly thicker and larger than
hex nuts and hex jam nuts. They are generally used for large diameter bolts.
Some important notes from the ASME B18.2.2:
- The diameter range of hex nuts and hex jam nuts is from ¼ inch to 1 1/2 inches according to
standard. For heavy hex nuts and heavy hex jam nuts, the range is from ¼ inch to 4 inches.
- Threads shall be Unified inch coarse, fine or 8 thread series with tolerance class of 2B (UNC, UNF, or UN-8).
- Unless otherwise specified, chemical and mechanical properties of steel nuts shall conform
with ASTM A563 Grade A, Carbon and Alloy Steel Nuts; or
Grade 2 of SAE J995, Mechanical and Material Requirements for Steel Nuts. Nuts of
other materials such as stainless steel, brass, bronze, and aluminum
alloys shall have properties as agreed upon between the manufacturer and purchaser.
The properties for nuts of several grades of stainless steel alloys are
covered in ASTM F 594, and of several nonferrous materials in the ASTM F 467.
- Hex nuts and hex jam nuts in sizes 5/8 in. (for heavy ones, this size is 7/16 in.) nominal size and smaller shall
be double chamfered. Larger size nuts shall be double chamfered or have washer
faced bearing surface and chamfered top.
Unified Screw Thread: A thread
form used by the United Kingdom, Canada, and the United States to obtain screw
thread interchangeability among these three nations. It has 60° thread angle and
dimensions are stated in inch units.
UN form screw threads: The UN
thread is intended for general purpose fastening operations.
UNC (Unified National Coarse):
Most commonly used type for general engineering applications. This thread form
is used in materials with low tensile strength which makes threads more
resistance against stripping (internal threads) .UNC give possibility for quick assembly.
UNF (Unified National Fine): External
threads of this Fine Series have greater tensile stress area than comparable sizes of the
coarse series. The Fine series is suitable when the resistance to stripping of both external
and mating internal threads equals or exceeds the tensile load carrying capacity of the
externally threaded member. It is also used where the length of engagement
is short, where a smaller lead angle is desired, where the wall thickness demands a fine
pitch, or where finer adjustment is needed.
Thread class: A classification system to classify the threads for
interchangeability and manufacturability. Class 1 threads are loosely fitting
thread and used for ease of assembly. Most commonly used class is 2 and this
class is designed for general use. Class 3 is used for closer tolerances.
Thread Gages and Gauging : Specifications and dimensions for the gages used on Unified inch screw thread is defined in the ANSI/ASME B1.2-1983 standard.
Types of gages including thread plug gages, snap gages, thread ring gages and
plain diameter gages for internal and external threads are covered in same
standard. Screw thread gauging systems for acceptability is covered in the ASME